Safety assembly for power presses



Nov. 4, '1952 P. H. DANLY SAFETY ASSEMBLY FOR POWER PRESSES 3 Sheets-Sheet 1 Filed March 19, 1949 Y E E m .l A

INVENTOR. PH/LO H. DHNL Y Nov. 4, 1952 P. H. DANLY SAFETY ASSEMBLY FOR POWER PRESSES 3 Sheets-Sheet 2 Filed March 19, 1949 v. u Y J. R mm N W H. 8 N D Z 0 I Iv Z H L n M a P HTTOENEY Nov. 4, 1952 P. H. DANLY SAFETY ASSEMBLY FOR POWER PRESSES 3 Sheets-Sheet 3 Filed March 19, 1949 Zoo INVENTOR. PH/LO H. DIM/LY E BY Patented Nov. 4, 1952 SAFETY ASSEMBLY FOR POWER PRESSES Philo H. Danly, Hinsdale, Ill., assignor to Danly Machine Specialties, Inc., Chicago, Ill., a corporation of Illinois Application March 19, 1949, Serial No. 82,421

8 Claims.

My invention relates to a safety assembly for power presses, and more particularly to an improved means for preventing the overloading of a power press in such a manner as to prevent injury to the working parts of the press.

Power presses are massive pieces of machinery used in metal shaping operations in conjunction with dies. The press comprises a frame with a reciprocating ram adapted to force the dies to the result that an eccentric shaft is bent or tie rods ruptured or strained. This may be occasioned by improper adjustment of the throw of the press ram or by accidentally using two sheets of metal instead of one, or by attempting to work upon metal of heavier gauge than that to which the press is designed, or otherwise subject the press to an overload. When this occurs a major repair job requiring time and expense is neces- 5 sary. When the press forms part of the production line, the whole production line is shut down during the period in which the press is being repaired.

One object of my invention is to provide a safety construction which will sense stresses placed upon the press and automatically unclutch the flywheel from driving engagementv with the press gear train whenever the stress "exceeds a predetermined limit.

Another object of my invention is ta-provide a safety assembly for power presses which automatically stops the press when the working load upon the press exceeds a predetermined limit, and will prevent the press from being operated again without a proper adjustment.

A further object of my invention is to provide a safety assembly for power presses of the tie rod construction, which will automatically place a proper tension upon the tie rods, thereby insuring accuracy of press operations.

Other and further objects of my invention will appear from the following description:

In the accompanying drawings, which form part of the instant specification, and which are to be read in conjunction therewith, and which have like reference numerals used to indicate like parts in the various views:

Fig. 1 is a perspective View of a tie rod power press with parts broken away.

Fig. 2 is a sectional view drawn on'an? enlarged 2 scale, showing the bottom of one of the tie rods.

Fig. 3 is a diagrammatic view, showing a safety assembly containing one embodiment of my invention.

Fig. 4 is a fragmentary diagrammatic view, showing a limit switch air pump construction in the combination.

Fig. 5 is a fragmentary diagrammatic view similar to Fig. 4, showing the use of a spring pump and intensifier instead of the pump and accumulator arrangement shown in Fig. 3.

In general, my invention contemplates the provision of means responsive to the thrust created during the working cycle of the press, such that when a predetermined thrust is exceeded, means are actuated to operate the clutch to disengage it from the power means and automatically to set the brake, thereby relieving the stress. While the means responsive to the thrust may be placed in the bolster of the press, the ram, the main eccentric or shaft bearing blocks, I prefer to associate the thrust responsive means with the tie rods of the press. Normally tie rods are tightened so that they are under a predetermined stress in order to prevent theelasticity of the tie rod from permitting a separation of the press parts during the working cycle. This is normally done by heating the tie rods so that they will expand, and then tightening the tie rod nuts while the tie rods are in expanded condition. When the tie rods shrink upon cooling, a predetermined stress is placed upon them. Changes in temperature will vary this stress and frequently tie rods may become unevenly stressed, due to the rather empirical nature of the heating and shrinking operation. In my invention I stress the tie rods by hydraulic cylinders which form an integral part of my safety assembly. The arrangement is such that when the hydraulic safety cylinders normally stressing the tie rods are subjected to an increased stress, the increased hydraulic pressure will actuate a switch to operate the clutch to release it. The clutch will remain in an inoperative condition until the pressure is lowered to a predetermined level. Then, too, I provide means for preventing the operation of the press unless the tie rods are stressed to a predetermined level. In this manner my safety accomplishes not only release for overloads but prevents the operation of press with improperly tensioned tie rods. Means are provided in my assembly for maintaining the hydraulic pressure upon the tie rod safety cylinders at a predetermined level.

More particularly referring now to the drawings, the press shown generally in Fig. 1 comprises a crown 6, side portions 1, and a base 8. These are held in assembled position by a plurality of tie rods l0, 12, M, and I6. A ram I8 is adapted to be reciprocated by mechanism positioned in the crown and well known to the art. A bolster 20 supported by the base 8 is provided. Co-oper- 3 ating die are secured to the ram I8 and the bolster 20.

The rod hydraulic safety cylinder may be best seen by reference to Fig. 2, in which a cylinder 22 is adapted to seat against the base member 8. The end of a tie rod I2 carries a. piston 24, which is secured thereto by means of a nut 26. Suitable hydraulic packing 28 is carried by the piston 24 and retained by a packing retainer ring 30, held in position by bolts 32. The cylinder is provided with a packing 34 and held in position by a packing retaining ring 36, secured by bolts 38. Hydraulic fluid is admitted into the cylinder through the bore 40. Hydraulic fluid which leaks by the packing 34 passes through drain opening 42 into a collecting pan 44 provided with a drain opening 46.

Referring now to Fig. 3, in which the four tie rods I0, I2, I4, and I6 are shown in hydraulic cylinders 22, 48, 50 and 52, I have shown the hydraulic pistons 54, 24, 56 and 58, secured to the tie rods by respective nuts 60, 26, 62 and 64. A hydraulic fluid manifold 66 communicates with a pipe 68 to which hydraulic fluid is supplied from an accumulator 10. The accumulator 10 has its upper part filled with entrapped air 12 and its lower portion filled with hydraulic fluid 14, supplied to it from hydraulic fluid reservoir 16 by a pump 16. The pump 18 is normally driven by a motor 80 and takes suction from the reservoir 16 through pipe 82, pumping fluid through pipe 84, through a pressure responsive means 86, through pipe 88, past check valve 90, through pipe 92, past valve 94, which is normally open, through pipe 96 to the accumulator 10. sive means is adapted to actuate a switch 98 to close the circuit from ground I through a solenoid I02, to a source of potential connected at I04. The arrangement is such that as soon as accumulator pressure reaches the predetermined limit, the switch 98 will operate to interrupt the circuit to motor 80, through conductors I06 and I01. The pressure in the accumulator is communicated through pipe I00 to a pressure switch H0. The arrangement is such that whenever the pressure in the accumulator 10 drops below a predetermined limit, the switch I I0 will operate to start the motor 80. It will be observed that the check valve 90 prevents the pressure from accumulator 10 from operating the pressure responsive device 86 through pipe 88. As soon as the motor 80 stops, excess pressure leaks 01f from pressure responsive device 86 through pipe I I2, permitting the pressure responsive device 86 to place the switch 98 in a position to close the motor circuit. The motor circuit, however, remain in an open position du to the pressure in the accumulator, communicating through pipe I08 to pressure switch H0. When the pressure drops below the predetermined point, the closing of switch H0 permits the motor to operate again, restoring the desired pressure in accumulator 10.

The hydraulic fluid in the accumulator 18 is enforced by the entrapped air 12 through pipe 68 to the manifold 66. Whence, it feeds the hydraulic safety cylinder 46 via pipe I I4, the safety hydraulic cylinder 22 via pip I I 6-, the safety hydraulic cylinder 58 via pipe I I8 and the hydraulic safety cylinder 52 via pipe I 20. The hydraulic fluid in the cylinders tensions the tie rods to the predetermined amount. It will be seen further that all of the tie rods are equally tensioned and this tension is predetermined to the desired amount. Any hydraulic fluid which leaks by the The pressure respon- I26 and I21 to the drain manifold I28.

tie rod packings drains through pipes I22, I24,

Any hydraulic fluid which leaks by the piston packings drains through pipes I30, I32, I34 and I36 to the drain manifold I28. A drain pipe I40 provides communication between the drain manifold I20 and the hydraulic fluid reservoir 16.

Since thepressure manifold 66 is always in communication with the accumulator 10, it will be readily noted that the hydraulic pressure is maintained upon the tie rods despite seepages. A cylinder I42 communicates with the manifold 66 through a pipe I44. A piston I46 is normally urged downwardly by a spring I48. The piston rod I50 carries a circuit making member I 52 adapted to close a circuit across contacts I54 and I56 through a solenoid I58. The solenoid armature I60 is normally urged upwardly by a spring I62 adapted to hold a switch I64, to complete a circuit through contact points I 66 and I68. The clutch operating circuit which governs the engagement of the press clutch is adapted to be interrupted by the switch I64. Whenever the press is subjected to an excessive strain, the pistons 24, 54, 56 and. 58, or one of them, will move upwardly increasing the hydraulic pressure in the manifold 66. When this pressure increases to a point governed by the compression of spring I48, the piston I46 will move upwardly to close the circuit through contacts I54 and I56, thus breaking the circuit which operates the clutch, permitting the clutch to be released and the brake of the press to be set by a construction well known to the art.

As a typical example, the switch I52 is set to make contact at 2200 lbs. per sq. inch. The contact thus made will be maintained until the pres sure drops to 1400 lbs. per sq. inch.

A second hydraulic cylinder I10 communicates with manifold 66 through a pipe I12, the communication being above a piston I14 positioned within the cylinder I10. A switch member I16 is carried by the piston rod I 18. A spring I normally urges the switch member I16 to make contact with contact points I02 and I84. Contact points I82 and I84 are in parallel with contact points I54 and I 56, so that whenever the circuit through the solenoid I 58 is completed by the switch member I16, the clutch operating circuit will be interrupted. The pressure within the manifold 66 normally holds the switch I16 in open position. The arrangement is such that whenever the manifold pressure is too low, which might be occasioned for example by a rupture of the systems piping, the press clutch will be automatically moved to releasing position. The switch I16 is set to make contact when the pressure drops to say 1800 lbs. per sq. inch and to reopen when the pressure rises to say 2,000 lbs. per square inch. In order to prevent the undue strain placed on the hydraulic piping or the tie rods, in event the pump control fails to operate, or by an excess stress upon the press, I provide a pressure relief valve I86 adapted to open to relieve the pressure in the system, say at 2300 lbs. per sq. inch. This is an added safety feature in event the pressure switch I52 fails to operate. In this case, the pressure relief valve I86 will open to relieve the hydraulic pressure in the system, thus the pressure switch I16 will be brought into operation. The hydraulic fluid will drain through pipe I88 to the hydraulic fluid reservoir 16.

The valve I90 is normally closed. It will be noted that the pressure switch I52 is set in the example given to cut the clutch out at 2200 lbs. per sq, inch, and to cut the clutch in at 1400 lbs. per -:sq. inch. Once the pressure has exceeded thelimit set, it will be necessary to reduce the pressure in the hydraulic system to below the clutch cut in pressure, in order to place the system again in operative condition. This isdone by opening the valve I90 and bleeding hydraulic fluid through pipe I92 into the reservoir I6 until the pressure drops below the cut in pressure. Before this is done the valve 94 is closed to prevent: loss of the pressure in the accumulator I0. Aiterthe pressure has fallen to a point at which the: switch I52 opened and the clutch is again cut-in, the valve I90 is closed and the valve 94 opened. The knife switch I94 is opened when valve94 is closed to interrupt the motor circuit 80. After the valve 94 is opened the knife switch I94 is closed and the pressure in the system is restored and again placed in operative condition.

Referring now to Figure 4, I have shown a construction having a limit switch air pump which enables me to eliminate the use of an accumulator. A source of compressed air under pressure is led through pipe 200 to a four-way valve 202 operated by an armature 204 and a solenoid 206. The arrangement is such that air may be fed through pipe 208 to the cylinder 2I0 above the piston 2I2. In this case air will exhaus t; through pipe 2I4, through the valve 202 and out of the exhaust 2 I6. As the piston travels downwardly it will make contact with operating member 2I8 to actuate switch 220. This energizes the solenoid 206 to operate the valve 202, so that pipe 2I4 is now placed in communication with -.the compressed air source and pipe 208 is connected with the exhaust 2I6. The piston will travel" in the opposite direction until contact is made by it with operating member 222 to actuate a switch 224 to energize another winding of the solenoid 206. The valve 202 will then be placed in aposition so that pipe 208 is again placed in communication with the compressed air source and pipe 2I4 is again placed in communication with exhaust pipe 2 I 6. The reservoir 226 is filled with oil and open to the atmosphere. H2 is provided with a plunger 228, operating in a cylinder 230. When the plunger moves upwardly, check valve 232 seats and oil is drawn under atmospheric pressure through pipe 234,

pastcheck valve 236, flowing through pipe 238 into the cylinder 230. When the stroke reverses, check valve 236 seats and valve 232 opens so that oilv ,is pumped through pipe 68, which corresponds to pipe 68 of Fig. 3. It will be observed that due to the difference in area between the air piston 2I2 and the hydraulic plunger 228, that a large mechanical advantage is obtained and-high pressures easily achieved. The pressure of compressed air above the piston 2I2 will urge this air piston downwardly, maintaining a pressure on the system similar to the accumulator pressure. Inasmuch as the seepages through the packings are slow and the volumes of liquid handled small, the system in Fig. 4 operates satisfactorily.

In Fig. 5 I have shown still another method of maintaining the hydraulic pressure of the system, in which I employed a spring pump and intensifier. The housing 300 contains a spring 302, normally urging a plunger 394 to the left, as

The piston viewed in Fig. 5. The plunger is provided with a stem 306, having a follower plate 308. A cam 3 I 0, is adapted to be rotated by any suitable means, as for example, from the working parts of the press. When the plunger moves to the right under the action of the cam 3I0, the check valve 3I2 seats and check valve 3 I4 will open to permit hydraulic fluid to be withdrawn from the reservoir 3 I6 into the pump chamber. As the plunger moves to the left under the action of the spring 302, check valve 3I4 seats and check valve 3I2 opens, pumping oil through pipe 68 which cor responds to pipe 68 of Fig. 3. The entire hydraulic system is under the pressure of plunger 304, which is in turn under pressure of the spring 302. Normally there will be very little leakage of hydraulic fluid, so that the cam 3I0 will have to do very little work.

Inasmuch as I employ the switch I16 to cut out the clutch when the pressure is below a desired point, it will be impossible to run the press, and hence, the cam 3I0 will not rotate if it is connected to a working part of the press, as I proposed. In order that I may place the press in operative condition, I provide a hand pump 320 operated by a hand lever 322. The pump 320 is adapted to take suction through pipe 324 from the reservoir H6, and to deliver hydraulic fluid through pipe 326, past check valve 328 to pipe 68, in order to bring the system up to pressure. The press may then operate and the spring pump will then take charge and maintain the system at the desired pressure.

It will be seen that I have accomplished the objects of my invention. I have provided a safety construction which will sense stresses placed upon the press in excess of those desired and automatically unclutch the flywheel from driving engagement with the press gear train whenever the stress exceeds a predetermined limit. I have provided a safety construction which will stop the press automatically when subjected to an overload and will prevent the press from being operated again until a corrective aCtiOn is taken. I have provided a safety assembly for power presses of the tie rod type which will automatically place the proper tension upon the tie rods and thus assist in insuring accuracy of press operations.

It will be understood that certain features and sub-combinations are of utility and may be employed without reference to other features and sub-combinations. This is contemplated by and is within the scope of my claims. It is further obvious that various changes may be made in details within the scope of my claims without departing from the spirit of my invention. It is, therefore, to be understood that my invention is not to be limited to the specific details shown and described.

Having thus described my invention, What I claim is:

l. A safety assembly for power presses including in combination a power press, a member adapted to be subjected to stress during the working cycle of the press, a hydraulic piston for balancing the stress in the member, means for applyin hydraulic pressure to the hydraulic piston, means for maintaining the hydraulic pressure at a predetermined point including an accumulator containing a quantity of compressed gas and hydraulic fluid whereby the hydraulic fluid is subjected to the pressure of the compressed gas, a pump for pumping hydraulic fluid into the accumulator, pressure responsive means for controlling the pump to start the same whenever the pressure in the hydraulic system falls below a predetermined point and means responsive to an increase in hydraulic pressure created by stress in the member beyond a predetermined point for stopping the operation of the press.

2. A safety assembly for power presses having tie rods including in combination a hydraulic cylinder, a piston within the cylinder, means for securing said piston to said tie rod, a hydraulic system for applying a predetermined hydraulic pressure to said piston to stress said tie rod to a desired point and means responsive to the increase of hydraulic pressure within the hydraulic system beyond a predetermined point for stopping the operation of the press, said hydraulic system including an accumulator, means providing communication between said accumulator and the hydraulic piston, said accumulator containing a quantity of compressed gas, a hydraulic fluid reservoir, a pump, means responsive to the pressure in the system for operating the pump to pump hydraulic fluid from the reservoir to the accumulator whenever the pressure falls below a predetermined point and fluid pressure means responsive to the pressure in the hydraulic system for stopping the pump whenever the pressure in the hydraulic system reaches a predetermined point.

3. A safety assembly for power presses having tie rods including in combination a hydraulic cylinder, 2. piston within the cylinder, means for securing the piston to the tie rod, a hydraulic system for applying a predetermined hydraulic pressure to the piston to stress the tie rod to a desired point, an electrical control system for starting and stopping the press having a control switch included therein for controlling the same, a solenoid for controlling the switch to operate the control circuit to stop the press, a circuit for energizing the solenoid including a normally open switch, a spring for urging said switch to open position, a second hydraulic cylinder, a second hydraulic piston, means providing communication between the hydraulic cylinder and the hydraulic system whereby an increase in pressure in the hydraulic system beyond a predetermined point will move the second piston against the action of the spring to close the switch to energize the solenoid to de-energize the control system to stop the press.

4. A safety assembly for power presses having tie rods including in combination a hydraulic cylinder, a piston within the cylinder, means for securing the piston to the tie rod, a hydraulic system for applying a predetermined hydraulic pressure to the piston to stress the tie rod to a desired point, an electrical control system for starting and stopping the press having a control switch included therein for controlling the same, a solenoid for controlling the switch to operate the control circuit to stop the press, a circuit for energizing the solenoid including a normally closed switch and a spring for urging said switch to closed position, a second hydraulic cylinder, a second hydraulic piston, means providing communication between the hydraulic cylinder and the hydraulic system whereby a predetermined pressure in the hydraulic system will move said switch against the action of said spring to open said normally closed switch, the construction being such that a reduction in pressure of the hydraulic system will permit the spring to move the switch to closed position to energize the solenoid to stop the press.

5. A safety assembly for power presses having tie rods including in combination a hydraulic cylinder, a piston within the cylinder, means for securing the piston to the tie rod, a hydraulic system for applying a predetermined hydraulic pressure to the piston to stress the tie rod to a desired point, an electrical control system for controlling the press including a switch forstopping the press, a solenoid for operating the switch to stop the press, a control circuit for the solenoid including a pair of switches connected in parallel whereby the closing of either switch will energize the solenoid, a second hydraulic cylinder, a second hydraulic piston within the second hydraulic cylinder, means responsive to th movement of the second hydraulic piston for operating one of said pair of switches, means for biasing the second hydraulic piston to normally open position, means providing communication between the hydraulic system and the second hydraulic cylinder opposing'the biasing means whereby upon an increase of hydraulic pressure beyond a predetermined point the second hydraulic piston will move against the biasing means to close said one of the parallel connected switches to energize the solenoid to stop the press, a third hydraulic cylinder, a third hydraulic piston, means responsive to the movement of the third hydraulic piston for operating the second parallel connected switch, means for biasing the third hydraulic piston normally to move the switch to closed position, means providing communication between the hydraulic system and the third hydraulic cylinder to oppose the biasing means to move the second parallel connected switch to open position, the construction being such that when the pressure in the hydraulic system falls below a predetermined point the biasing means will move the second parallel connected switch to closed position to energize the solenoid to stop the press.

6. A safety assembly as in claim 3 in which there are a plurality of tie rods, a plurality of hydraulic cylinders and a plurality of respective pistons within the respective cylinders, means for securing respective tie rods to the pistons, said hydraulic system including means for placing a common predetermined hydraulic pressure upon each of the respective pistons.

7. A safety assembly as in claim 3 in which the hydraulic system includes pressure relief means and means for relieving the pressure in the system whenever it passes a predetermined point.

8. A safety assembly as in claim 3 in which the hydraulic system includes a hydraulic fluid reservoir, means for supplying hydraulic fluid from the reservoir to the hydraulic system, packing for the first hydraulic piston, packing for the hydraulic cylinder associated therewith and means for returning hydraulic fluid seeping past the packings to the hydraulic reservoir.

PHILO H. DANLY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Germany Aug. 2, 1933 

